An ankle-foot orthosis (also commonly referred to in the art simply as an AFO) is an orthotic device that firmly surrounds at least a portion of the ankle and foot of a patient. An ankle-foot orthosis is commonly constructed as a relatively lightweight and rigid brace that supports the lower leg and foot of a patient and serves to, among other things, properly control the position and motion of the ankle and foot of the patient through each gait cycle, compensate for muscular weakness and/or correct deformities. For this reason, ankle-foot orthotic devices are commonly utilized in the treatment of patients suffering from a wide variety of muscular disorders, such as stroke patients.
One type of ankle-foot orthosis which is well known in the art is constructed as a rigid brace which utilizes a solid ankle design. In other words, the brace includes an enlarged, solid piece of rigid material, such as polypropylene, that wraps around the majority of the foot, ankle and lower leg of the patient. Although useful in providing the patient with the requisite degree of stabilization for adequate weight support, ankle-foot orthotics that rely on a unitary, solid design inherently lack the flexibility to assist the patient to closely simulate the proper gait cycle.
Specifically, a proper gait cycle consists of the events from first heel strike (i.e., contact of the heel onto the ground) to second heel strike on the same foot. In the industry, the gait cycle is commonly separated into two principal phases: (1) the stance phase—the weight bearing portion of the gait cycle (i.e., the period of direct contact of the foot against the ground), and (2) the swing phase—the non-weight bearing portion of the gait cycle (i.e., the period in which the foot swings above the ground, from toe-off to subsequent heel strike). As can be appreciated, 62% of gait is weight-bearing, whereas 38% of gait is non-weight bearing. Accordingly, it is to be understood that proper lower extremity support is essential to a patient with physical limitations.
The stance phase of the proper walking gait cycle includes five defined stages: (1) initial contact—when the heel of the patient first strikes the ground (i.e., initial heel strike), (2) loading response—the period from when weight bears on the loaded extremity after initial contact until the opposite foot is lifted for the swing phase, (3) mid stance—the first half of single limb support from when the opposite foot is lifted until weight is disposed over the fore foot, (4) terminal stance—the period from when heel rises until the opposite foot strikes the ground, and (5) pre swing—the period from when the initial contact of the opposite foot to toe-off on the first foot.
It is to be understood that the lower extremity of a patient includes three natural rockers to assist in the complex kinetic chain required to perform the stance phase. Specifically, the lower extremity includes (1) a heel rocker that acts as a fulcrum as the foot rolls into plantar flexion by allowing the limb to roll forward as body weight is dropped thereon after the initial strike, with pre-tibial muscles decelerating the foot drop and drawing the proximal end of the tibia forward, (2) an ankle rocker that acts as a fulcrum as the tibia moves forward relative to the foot once the forefoot strikes the ground, with tibia progression controlled by eccentric contraction of the soleus muscle in the back part of the lower leg, and (3) a forefoot rocker that acts as a fulcrum as tibial progression advances to toe-off (i.e., as the heel rises, the fulcrum for the tibia as advancement shifts to the metatarsal heads, with progression accelerated as body weight falls beyond the area of foot support).
As referenced briefly above, it is often desirable for an ankle-foot orthosis to closely simulate the proper motion of the treated lower extremity throughout the gait cycle. Because the gait cycle requires a relatively complex kinetic chain of movement in the lower extremity, the majority of which is load-bearing, it is often important that an ankle-foot orthosis be designed to promote the proper sequence of complex movement.
In particular, it has been found that the heel strike is a traumatic event that creates substantial amount of shock, or force, in the heel. However, traditional AFOs that rely upon a solid design fail, among other things, to properly decelerate the heel upon initial heel strike to create a smooth roll and thereby simulate proper movement of the heel rocker. Rather, solid ankle design AFOs tend to throw the weight of the patient forward and/or outward in a rapid manner and without proper control, which is highly undesirable.